Most of today's processors incorporate a temperature sensor used for thermal monitoring. Often, the thermal monitor is integrated into the processor silicon. It includes a temperature sensing circuit and means for generating a signal (PROCHOT) that indicates that the processor has reached a maximum safe operating temperature. The processor may also include control circuitry that can automatically reduce processor speed and thereby reduce power consumption while the processor temperature is high.
In addition to the PROCHOT signal, or perhaps, alternatively, processors may also include an on-die diode that monitors the die temperature (junction temperature). If the temperature rises above a predetermined threshold, the processor shuts down. More specifically, when the junction temperature rises above a certain temperature (i.e., 135° C. for the Pentium III processor), the processor stops executing all instructions. The processor signals this condition to the rest of the system with a THERMTRIP (thermal trip) signal. The processor will remain stopped until a reset signal goes active via a restart or reset switch.